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OPINION input requested

Ref: Discussion of SuperHots,

I expressed the following OPINION If I'm wrong, don't pull any punches, just tell me where I went wrong.

bob

In my OPINION, whether the centerline of the crankshaft is directly ON the published thrust line,, or a bit above or below that line should have relatively little effect on how the plane operates. the firewall on this plane is relatively tiny, so to get more than around 1/2 inch away from the published number is going to be a bit difficult.

If my OPINION is wrong, perhaps some of the folks who understand it better could jump in and tell me where my reasoning is at fault.

Reply to
Bob Cowell
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On Tue, 15 May 2007 09:42:31 -0500, Bob Cowell wrote in :

Agreed 100%.

I'll take your word for that.

Evidence for why I think the centerline of the crankshaft doesn't have to be on the centerline of the fuselage: any number of amphibians and gliders that have the thrustline (which follows the engine wherever it goes) well above the centerline and center of mass of the aircraft.

The engines are mounted on pods or on the vertical stab.

So airplanes can be made to fly with that kind of arrangment.

Having said that, it also seems reasonable to think that as you move the thrustline above the centerline and center of mass of the aircraft that stuff will happen to the flight characteristics. Whether we would notice the change depends a lot on the quality of the pilots and the design of the aircraft.

I'll bet that a 1/2" change up or down on the firewall could be trimmed out without any difficulty and that after trimming no one could tell the difference. There

**has** to be a calculable difference in the thrust vectors because of the difference in location, but that does not mean that it would be noticeable from the ground.

Marty

Reply to
Martin X. Moleski, SJ

I suspect it won't make a heck of a lot of difference. If you're flying for sport, it probably won't be significant. If you're looking for all-out precision aerobatic performance, then that 'not a heck of a lot of difference' may be more than enough to worry about, at least once.

Reply to
Tim Wescott

Depends on what you mean by 'relatively little'.

Its certainly enough to make e.g. a pattern plane completely untrimmable for precision flight.

Its barely going to affect an average sort of sport model, which is like that (untrimmable for precision flight) out of the box anyway..

Reply to
The Natural Philosopher

For the average run of the mill bird, you are correct. For a precision aircraft, that is a disaster. The issue is thrust vector changes when the throttle changes. Think about the old flat bottomed wing trainers and the down thrust built in and you will realize the impact of that 'off center line' installation.

Reply to
Six_O'Clock_High

Reply to
Paul Ryan

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